Association of <sup>34</sup>S‐depleted pyrite layers with negative carbonate <i>δ</i><sup>13</sup>C excursions at the Permian‐Triassic boundary: Evidence for upwelling of sulfidic deep‐ocean water masses
Bibliographic record
Abstract
A marine Permian‐Triassic boundary (PTB) section at Nhi Tao, Vietnam, contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite S‐ ( δ 34 S py ) and carbonate C‐isotopic compositions ( δ 13 C carb ). The first and largest of the events that precipitated these pyritic horizons was coincident with the Late Permian mass extinction, while subsequent events were generally smaller and occurred at quasiperiodic intervals of ∼20 to 30 ka. A near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters, among other considerations, argues against a diagenetic control for these relationships. Rather, the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep‐ocean waters containing 34 S‐depleted hydrogen sulfide and 13 C‐depleted dissolved inorganic carbon. The sulfide δ 34 S record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite (formed via in situ bacterial sulfate reduction) with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes. Although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the Late Permian marine mass extinction, this is the first study to (1) document patterns of pyrite‐ δ 13 C carb covariation that strongly support upwelling as a major process at the PTB and (2) provide evidence of multiple, quasiperiodic upwelling events that may reflect reinvigoration of global‐ocean overturn following a prolonged interval of Late Permian deep‐ocean stagnation.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".